A Map implementation that stores its contents in a single
array. This approach is significantly faster for small sets of
data than the use of a HashMap or Hashtable, though potentially
much slower for very large sets.

ArrayMap is optimized for many-reads-few-write. In particular,
it reallocates its array on any insertion or deletion.

ArrayMap also includes a series of static methods for managing the
Object array. These may be used in place of instantiating an
ArrayMap for clients that don't need a Map implementation.
Clients using these methods must be careful to store the returned
Object array on any mutator method. They also must provide their
own synchronization, if needed. When using these static methods,
clients can opt to search for objects by identity (via
getByIdentity()) instead of equality, while the static
get() method will try identity before equality. This
latter approach is extremely fast but still safe for retrieval of
Strings that have all been interned, especially if misses are
infrequent (since misses do require a scan using Object.equals()).
It's worth remembering that String constants are always interned,
as required by the language specification.